Idiopathic pulmonary fibrosis (IPF) is a progressive and usually fatal disease of unknown etiology. The median survival after diagnosis is approximately 3 years, with outcomes being largely unaffected by current therapies. Improved understanding of the biologic processes involved in development of lung fibrosis, and more complete identification of the molecular mediators driving these processes, are critically needed to develop effective new therapies. We have recently demonstrated that the potent lipid mediator lysophosphatidic acid (LPA) is critically required for the development of pulmonary fibrosis in mice following bleomycin-induced lung injury. In this model, levels of LPA increase in bronchoalveolar lavage (BAL) fluid following bleomycin challenge, and mice lacking LPA1, one of LPA's receptors, are markedly protected from fibrosis and mortality. We have also demonstrated that LPA levels are increased in the BAL fluid of patients with established IPF, that LPA1 is highly expressed by fibroblasts recovered from IPF BAL, and that pharmacological antagonism of LPA1 markedly reduces fibroblast responses ex vivo to the chemotactic activity of IPF BAL. These results suggest that the LPA pathway may be relevant to the pathogenesis of pulmonary fibrosis in humans as well as mice. The studies proposed in this application are designed to address what we believe are the most important questions raised by our identification of LPA as a mediator of lung fibrosis. In Aim 1, we will determine whether pharmacological inhibition of the LPA pathway can inhibit the development or progression of pulmonary fibrosis in vivo, by using two novel LPA pathway chemical inhibitors in the bleomycin model. In Aim 2, we will determine whether the LPA pathway contributes to the development of IPF in humans, first by investigating whether LPA is responsible for fibroblast recruitment in a unique cohort of early stage "preclinical" pulmonary fibrosis patients. These patients are identified by screening asymptomatic members of familial pulmonary fibrosis kindreds. We will then take a genetic epidemiological approach to investigate whether the LPA pathway contributes to IPF pathogenesis, by determining whether polymorphisms in the genes of this pathway contribute to individuals'risk of developing IPF. In Aim 3, we will investigate the biological mechanism(s) that are responsible for the dramatic degree to which LPA1-deficient mice are protected from pulmonary fibrosis. In this aim, we will use the Cre-lox system of site-specific recombination to generate and study mice in which LPA1 expression is specifically deleted in fibroblasts, to determine whether fibroblast recruitment directed by the LPA pathway contributes to the development of fibrosis in the bleomycin model. We believe the experiments proposed in this application will both improve our understanding of the role of the LPA pathway in the development of pulmonary fibrosis, and determine whether targeting this pathway has the potential to be an effective new therapeutic strategy for IPF. PUBLIC HEALTH RELEVANCE: Idiopathic pulmonary fibrosis (IPF) is associated with unacceptably high morbidity and mortality. Improved understanding of the molecular mediators driving IPF pathogenesis is desperately needed in order to identify new therapeutic targets for this devastating disease. The proposed studies are designed to provide new insights into the role of the novel mediator lysophosphatidic acid (LPA) in the development of pulmonary fibrosis, and to provide new evidence that targeting the LPA pathway has the potential to be an effective therapeutic strategy for IPF.